Effect of gender on bone turnover in adult rats during simulated weightlessness

• Published in: Journal of applied physiology (1985) 2003-11, Vol.95 (5), p.1775-1780
• Main Authors: Hefferan, T. E, Evans, G. L, Lotinun, S, Zhang, M, Morey-Holton, E, Turner, R. T
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Bone Matrix - physiology; Bone Resorption - physiopathology; Bones; Collagen Type I - genetics; Female; Fundamental and applied biological sciences. Psychology; Gender; Hindlimb Suspension - physiology; Male; Osteocalcin - genetics; Osteonectin - genetics; Osteoporosis - physiopathology; Rats; Rats, Inbred F344; RNA, Messenger - analysis; Sex Characteristics; Space biology; Tibia - physiopathology; Weightlessness; Weightlessness Simulation
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00455.2002

1 Departments of Orthopedics, Biochemistry, and Molecular Biology, Mayo Clinic, Rochester, Minnesota 55905; and 2 National Aeronautics and Space Administration-Ames Research Center, Moffett Field, California 94035 Submitted 22 May 2002 ; accepted in final form 23 May 2003 Prologned spaceflight results in bone loss in astronauts, but there is considerable individual variation. The goal of this rat study was to determine whether gender influences bone loss during simulated weightlessness. Six-month-old Fisher 344 rats were hindlimb unweighted for 2 wk, after which the proximal tibiae were evaluated by histomorphometry. There were gender differences in tibia length, bone area, cancellous bone architecture, and bone formation. Compared with female rats, male rats had an 11.6% longer tibiae, a 27.8% greater cortical bone area, and a 37.6% greater trabecular separation. Conversely, female rats had greater cortical (316%) and cancellous (145%) bone formation rates, 28.6% more cancellous bone, and 30% greater trabecular number. Hindlimb unweighting resulted in large reductions in periosteal bone formation and mineral apposition rate in both genders. Unweighting also caused cancellous bone loss in both genders; trabecular number was decreased, and trabecular separation was increased. There was, however, no change in trabecular thickness in either gender. These architectural changes in cancellous bone were associated with decreases in bone formation and steady-state mRNA levels for bone matrix proteins and cancellous bone resorption. In conclusion, there are major gender-related differences in bone mass and turnover; however, the bone loss in hindlimb unweighted adult male and female rats appears to be due to similar mechanisms. rat bone; bone formation; bone resorption; spaceflight; disuse osteoporosis Address for reprint requests and other correspondence: R. T. Turner, Orthopedic Research, Rm. 3-69 Medical Science Bldg., Mayo Clinic, 200 First St. SW, Rochester, MN 55905 (E-mail: turner.russell{at}mayo.edu ).